Conventionally, as favorable water-resistant inkjet inks, inkjet inks of an oil soluble dyestuff dispersed or dissolved in a high-boiling solvent and those of an oil soluble dyestuff dissolved in a volatile solvent have been known. However, dyes are inferior in stability such as light stability comparing to pigments. Therefore, there was a demand for an ink containing a pigment as the colorant. However, it was difficult to stably disperse a pigment in an organic solvent and to assure stable dispersion and ejection. On the other hand, it was difficult to dry inks containing a high-boiling solvent by vaporization because the solvent is less volatile, and thus, such an ink could not be printed on a non-absorptive substrate.
An ink containing a volatile organic solvent can be favorably printed on a non-absorptive substrate, depending on the adhesiveness of the resin and the volatility of the solvent. However, the head nozzle face was dried very quickly due to the vaporization of the solvent, which requires frequent maintenance. In addition, an ink should be re-dissolved in solvent, and thus, the solvent resistance of the printing was insufficient in some cases.
In order to satisfy the above properties, inks containing non-volatile monomers that prevent the head from drying and are cured by irradiation of an active-energy ray were also used. Such active energy ray-curable inkjet inks are disclosed in Patent Documents 1 to 7, but none of the inks were practical enough, from the points of substrate adhesiveness, pigment dispersion, ejection stability, and storage stability.    Patent Document 1: Japanese Patent Application Laid-Open No. 5-214280    Patent Document 2: Japanese Patent Application Laid-Open No. 9-183929    Patent Document 3: Japanese Patent Application Laid-Open No. 2002-167537    Patent Document 4: Japanese Patent Application Laid-Open No. 2004-518787    Patent Document 5: Japanese Patent No. 3619778    Patent Document 6: Japanese Patent Application Laid-Open No. 2004-175906    Patent Document 7: Japanese Patent Application Laid-Open No. 2004-182808